vim-patch:8.2.0674: some source files are too big (#19959)

Problem:    Some source files are too big.
Solution:   Move text formatting functions to a new file. (Yegappan
            Lakshmanan, closes vim/vim#6021)
11abd09521

Cherry-pick set_can_cindent() from patch 8.1.2062.
Cherry-pick global old_indent from patch 8.2.2127.

src/nvim/indent.c

@@ -25,6 +25,7 @@
 #include "nvim/screen.h"
 #include "nvim/search.h"
 #include "nvim/strings.h"
+#include "nvim/textformat.h"
 #include "nvim/undo.h"
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS